1. Field of the Invention
This invention relates to a brake system for vehicles in which compensation for failure of one brake set may be provided by utilizing surplus braking capacity of another brake set.
2. Background of the Prior Art
With current designs for low-floor light rail vehicles (LRVs), space beneath each vehicle is at a premium. As a result, the friction brakes on these vehicles, which in the past were large enough to provide any braking the vehicle required, must be reduced in size to accommodate the now limited space beneath the vehicle and, therefore, must be underrated. LRVs typically have dynamic brakes which operate using the same motor that would propel the vehicle, and these brakes are used in conjunction with the friction brakes to decelerate the vehicle, thereby providing to the vehicle multiple brake sets.
However, since the friction braking alone cannot directly replace a loss of the dynamic braking, a brake failure compensation system is needed. This system will detect a loss of braking force in one brake set and attempt to compensate for that loss by passing the quantity of lost braking to another functional brake set which has surplus braking capacity. In this manner the vehicle may be decelerated at a desired rate despite the failure of a brake set.
U.S. Pat. No. 3,887,239 to Engle teaches a method for controlling the speed of a vehicle, such as a railway train, by applying a friction brake signal upon a command for braking. While a friction brake may be modulated to supplement an existing dynamic brake, this patent does not address compensation for brake failure but is directed toward controlling operational braking units thereby adjusting them to prevent or minimize wheel skidding.
U.S. Pat. No. 5,511,859 to Kade et al. discloses a dynamic and friction brake blend control system which consists of hydraulic friction brakes and a dynamic electric motor drive. The dynamic braking is blended with the hydraulic braking to achieve the desired braking; however, there is no discussion of compensating for the failure of any one brake.
A system is needed which is capable of utilizing the surplus capacity of the remaining operating brake sets in the event of the failure of one or more other brake sets.